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Bacteria – the Benign, the Bad and the Beautiful

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Bacteria – the Benign, the Bad and the Beautiful Bacteria – the benign, the bad and the beautiful. Facts : • Bacteria are present almost everywhere from deep in the earth's crust to the polar ice caps and oceans to inside the bodies of plants and animals. • There are more bacteria in your mouth than there are people in the world. • Babies are born with no bacteria in their bodies. • Electronics, cellphones, laptops, keyboards etc. hold a lot of bacteria. Single smartphone screens hold 18 times more bacteria than a toilet handle. • Smell of rain is caused by a bacteria called actinomycetes. • Sweat itself is odourless. It’s the bacteria on the skin that mingles with it and produces body odour. • Horseshoe crab blood is worth US $15000/ L due to its ability to detect bacteria. • Gonorrhea bacteria is the strongest creatures on the earth as they can pull 100,000 times their own weight. Introduction . Bacteria were discovered by Leeuwenhoek in 1676. They are the primitive forms of life. They are monerans and comprises a group of prokaryotic organisms which is characterized by: o Peptidoglycan wall o Compacted but naked DNA with attached mesosome o Reserve food material made up of glycogen and fats o Gas vacuoles may occur o All membranes bond cell organelles completely absent o 70S Ribosome occurs . They have varied forms of nutrition. Bacterial cell structure § Cell morphology Structure of a typical bacterial cell Cell Envelope Outer covering of protoplast of bacterial cell. The cell envelope of bacteria consist 3 components: • Glycocalyx • cell wall • plasma membrane Glycocalyx Some bacteria have an Glycocalyx gives sticky additional layer outside character to the cell. of the cell wall called It is not absolutely essential the Glycocalyx. for survival of bacteria. This outermost However it has several mucilaginous layer secondary functions: consist of non cellulosic • Prevention of polysaccharides with or desiccation without proteins. • Protection from It occurs as phagocytes • Slime layer when • Protection from toxic glycocalyx occur in chemicals and drugs the form of loose • Protection from viruses mucilage sheath • Attachment • Capsule when thick • Immunogenicity and tough mucilage • Virulence covering. Cell wall The bacterial cell wall differs from that of all other organisms by the presence of peptidoglycan which is located immediately outside of the cytoplasmic membrane. Peptidoglycan is made up of a polysaccharide backbone consisting of alternating N- Acetylmuramic acid (NAM) and N- acetylglucosamine (NAG) residues in equal amounts. Peptidoglycan is responsible for the rigidity of the bacterial cell wall and for the determination of cell Fig: The structure of peptidoglycan. shape. It is relatively porous and is not considered to be a permeability barrier for small substrates. Types of bacterial cell wall There are two main types of bacterial cell walls, those of gram-positive bacteria and those of gram-negative bacteria, which are differentiated by their Gram staining characteristics. Gram-positive cell walls are thick and Gram-negative cell walls are thin peptidoglycan layer adjacent to the cytoplasmic membrane. Peptidoglycan layer constitutes almost 95% of the cell wall in some gram-positive bacteria and as little as 5-10% of the cell wall in gram-negative bacteria. Fig: Structure of bacterial cell wall Cell membrane The plasma membrane or bacterial cytoplasmic membrane is composed of a phospholipid bilayer and thus has all of the general functions of a cell membrane. It is selectively permeable. It is metabolically active as it takes part in respiration, synthesis of lipids and cell wall Fig: Bacterial cell membrane components. Mesosome Multi-laminated structure formed invaginations of plasma membrane. Principal sites of respiratory enzymes. Coordinate nuclear & cytoplasmic division during binary fission. More prominent in Gram +ve bacteria. Fig : structure of mesosome Ribosome Bacteria and archaebacteria have smaller ribosomes, termed 70S ribosomes, which are composed of a small 30S subunit and large 50S subunit. The "S" stands for svedbergs, a unit used to measure how fast molecules move in a centrifuge Fig : structure of 70S ribosome Fig : nucleoid organisation in bacteria Plasmid Extra nuclear genetic elements consisting of DNA. Transmitted to daughter cells during binary fission. May be transferred from one bacterium to another. Not essential for life of the cell. Confer certain properties e.g. drug resistance, toxicity. Flagella Long (3to12µ),filamentous surface appendages. Organs of locomotion. Chemically, composed of proteins called flagellins. The number and distribution of flagella on th bacterial surface are characteristic for a given species- hence are useful in identifying and classifying bacteria. Flagella may serve as antigenic determinants(e.g.the H antigens of Gram-negative enteric bacteria). Presence shown by motility Fig : structure of flagella e.g.hanging drop preparation. Pilli and fimbriae Proteins filaments. Shorter and thinner: fimbriae Longer and fewer: pili Sex Pili : The filaments that are best known for their function in conjugation. Inclusion bodies Are reserve deposits of bacterial. Cells accumulate nutrient when they are plenty and use when deficient. Major Inclusion bodies are: • Gas vacuoles-allows for buoyancy . • Sulfur granules. • Polyphosphate granules. • Glycogen granules. • Lipid inclusion. • Magnetosomes. .
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